Unit and program for displaying map

ABSTRACT

The invention provides a map display unit including a first memory for storing map data and a drawing memory for drawing the map data and displaying display-area data and a display. The map display unit includes a unit to read and decompress compressed map data stored in blocks in a data storage medium and to store the decompressed map data in the first memory; a unit to draw the stored map data in the drawing memory; and a unit to determine the display area and to display the display-area data of the drawing area in the drawing memory on the display. When there is no display-area data in the first memory, compressed map data is read and decompressed from the data storage medium by the data decompression unit. The map display unit further includes an environmental change sensor and controllers to vary the color tone of the map data with the environmental change, thereby displaying easily viewable map data.

The disclosure of Japanese Patent Application No. 2002-232831 filed onAug. 9, 2002 and No. 2002-232830 filed on Aug. 9, 2002 including thespecification, drawings and abstract are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a unit and a program for displaying a map, theunit including a first memory for storing map data and a drawing memoryfor drawing the map data and displaying display-area data of a drawingarea in the drawing memory on a display while editing the map inaccordance with selected edit information.

2. Description of Related Art

In navigation systems, a map scroll operation is performed on a screento display a simulation route from the current location to a destinationon a map screen in sequence, to track-display the current location withthe actual traveling, and to set a starting point, a destination, and adetour on the map.

For example, there have been proposed navigation systems in which, whena map is scrolled with the current location and a route displayedthereon, a determination frame is placed inside a display area and thescrolling is controlled depending on whether a target point is present,thereby eliminating useless scroll operations (JP Publication No.2000-275050, paras [0011], [0055] and [0056], FIGS. 4–6).

Various data and various data constructions are used to display a map innavigation systems. One of the data used for map display is satellitephotograph data. Because the satellite photograph data is large in size,it is generally compressed (by Joint Photographic Experts Group method:JPEG, etc.) when stored in a map disc (storage medium). The compresseddata must be decompressed before such satellite photograph data isdisplayed.

The process for decompressing JPEG compressed data with highcompressibility takes a lot of time, thus posing the problem of too lowfollow-up capability to catch up the display when the current locationis tracked and scrolled using the satellite photograph data displayed bya car navigation system.

Various propositions have been put forth (JP Publications Nos. 5-018767,paras [0022]–[0026], FIG. 6 and 2000-283784, para [0025]) regarding mapdisplays in the car navigation systems, one of which is a system ofdisplaying a route guide map on a display screen such that theluminosity of the display screen and a color palette is changed withtime so as to prevent the display from becoming hard to view with achange in day-to-night ambient luminosity. However, it takes a lot ofprocessing time to change colors using the color palette, thus havingthe problem of taking a long time particularly when the number of colorsto be changed is large.

Another proposition has described a system in which two kinds ofsatellite photograph data for daytime and nighttime are stored in astorage medium and data is switched from daytime satellite photographdata to nighttime satellite photograph data in synchronization with acar lighting switch. The system, however, has the problem of requiring astorage medium for storing two pieces of satellite photograph data onthe same location thereby increasing the cost of the entire system.

SUMMARY OF THE INVENTION

The invention has been made to address the above problems. Accordingly,an object of the invention is to allow smooth scrolling of a map displayusing compressed data without delay in the display.

Another object of the invention is to allow an easily viewable displayresponding to differences in the environment using one piece of imagedata and to allow editing of various display images.

To this end, according to the invention, there is provided a map displayunit including a first memory for storing map data and a drawing memoryfor drawing the map data and displaying display-area data of a drawingarea in the drawing memory on a display. The map display unit includes adevice to read and decompress compressed map data stored in a datastorage medium and to store the decompressed map data in the firstmemory; a device to draw the map data stored in the first memory in thedrawing memory; and a device to determine the display area and todisplay the data on the display area of the drawing area in the drawingmemory on the display; wherein, when there is no display-area data inthe first memory, compressed map data including the display area is readout and decompressed from the data storage medium by the device to readand decompress map data.

According to an embodiment of the invention, the compressed map data israster data divided into blocks and having positional information foreach block.

According to an embodiment of the invention, when there is nodisplay-area data in the first memory, the compressed map data includingthe display area, which is read out from the data storage medium, iscompressed map data obtained on the basis of the positional informationof the compressed map data and the coordinates of the display area.

Further, according to the invention, there is provided a map displayunit including a first memory for storing map data and a drawing memoryfor drawing the map data and displaying display-area data of a drawingarea in the drawing memory on a display. The map display unit includes adevice to read and decompress compressed map data stored in a datastorage medium and to store the decompressed map data in the firstmemory; a device to draw the map data stored in the first memory in thedrawing memory; and a device to determine the display area and displaythe data on the display area of the drawing area in the drawing memoryon the display; wherein, when there is no display-area data in thedrawing area of the drawing memory, map data on the display area is readout from the first memory and is drawn in the drawing memory by thedevice to draw the map data.

Additionally, according to the invention, there is provided a mapdisplay unit including a first memory for storing map data and a drawingmemory for drawing the map data and displaying display-area data of adrawing area in the drawing memory on a display. The map display unitincludes a device to select and read out compressed map data anduncompressed map data from a data storage medium; a device to decompressthe compressed map data read out by the data-reading device and to storethe decompressed map data in the first memory; a device to draw eitherof the uncompressed map data read out by the data-reading device or themap data stored in the first memory in the drawing memory; a device todetermine the display area and display the data on the display area ofthe drawing area in the drawing memory on the display; and a device toswitch a map to be displayed; wherein the map selecting device switcheswhich of the uncompressed map data or the map data the drawing devicedraws in the drawing memory.

According to an embodiment of the invention, the map selecting deviceincludes a device to determine the velocity of a vehicle and switchesthe map to be displayed depending on whether the velocity has exceeded athreshold.

According to an embodiment of the invention, the compressed map data israster data and the uncompressed map data is vector data.

According to an embodiment of the invention, the raster data issatellite photograph data.

According to an embodiment of the invention, the device to decompressthe map data manages the use history of the map data stored in the firstmemory, erases the map data in early order, and stores the decompressedmap data in the first memory.

Also, according to the invention, there is provided a map displayprogram including the steps of reading and decompressing compressed mapdata stored in a data storage medium; storing the decompressed map datain a first memory; drawing the map data stored in the first memory in adrawing memory; and determining a display area and displaying data onthe display area of a drawing area in the drawing memory on a display.When there is no display-area data in the first memory in the step ofdisplaying the data on the display, the compressed map data includingthe display area is read out and decompressed from the data storagemedium in the step of reading and decompressing the compressed map data.

Further, according to the invention, there is provided a map displayunit including a storage device to store raster map data; a sensingdevice to sense a change in the environment; a control device to changethe color tone of the raster map data depending on the change in theenvironment sensed by the environmental-change sensing device; and adisplay device to display the map data changed by the control device.

According to an embodiment of the invention, the map data is dividedinto blocks and each of the divided raster data has positionalinformation on a representative point.

According to an embodiment of the invention, the sensing device sensesthe change in the environment on the basis of the information of theglobal positioning system (GPS).

According to an embodiment of the invention, the sensing devicedetermines whether the time is day or night depending on whether avehicle light is lit.

According to an embodiment of the invention, the sensing devicedetermines the current season on the basis of GPS information.

According to an embodiment of the invention, the control device changesthe RGB value of the map data on the basis of predetermined colorinformation and transmittance information.

According to an embodiment of the invention, the storage device furtherincludes vector map data and current-location-mark information, andwherein the control device overwrites vector map data on a destinationguidance route on the raster map data whose color tone has been changed.

According to an embodiment of the invention, the control device changesthe color tone of the raster map data when the map data is drawn in thedrawing memory.

According to an embodiment of the invention, the control means changesthe color tone of the raster map data drawn in the drawing memory whenthe map data is outputted to the display device.

And, according to the invention, there is provided a map display programfor displaying a map on the basis of raster map data stored in storagedevice and a change in the environment sensed by a sensing device forsensing a change in the environment. The map display program includesthe steps of sensing a change in the environment by the sensing device;changing the color tone of the raster map data depending on the changein the environment sensed in the step of sensing the change in theenvironment; and displaying the map data changed in the step of changingthe color tone.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter with reference to thedrawings in which:

FIG. 1 is an explanatory diagram of a map display unit according to anembodiment of the invention;

FIG. 2 is a block diagram of data stored in a map-data storage medium;

FIG. 3 is a schematic diagram of satellite photograph data;

FIG. 4 is a diagram showing the relationship among satellite photographdata on a data storage medium, satellite photograph data to bedecompressed on a first memory, and a display screen;

FIG. 5 is a flowchart for display processing;

FIG. 6 is an explanatory diagram of coordinate conversion processing byscrolling a display screen;

FIGS. 7(A) to 7(C) are diagrams for explaining examples of drawing anddisplay processing;

FIG. 8 is an explanatory diagram of an example of the process ofconverting a day-image satellite photograph to a night image;

FIG. 9 is an explanatory diagram of another example of the process ofconverting a day-image satellite photograph to a night image;

FIG. 10 is an explanatory diagram of an example of the process ofdisplaying a mark and a route on a satellite photograph;

FIG. 11 is a flowchart of a process for switching a display by using onelayer;

FIG. 12 is a flowchart of a process for switching a display by using twolayers;

FIG. 13 is a block diagram of a circuit for editing;

FIG. 14 is a block diagram of another circuit for performing editing;and

FIG. 15 is a block diagram of a car navigation system incorporating themap display unit according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings, reference numeral 1 denotes a data storage medium;numeral 2 denotes a data read-out section; numeral 3 denotes a datadecompressing section; numeral 4 denotes a first memory; numeral 5denotes a drawing section; numeral 6 denotes a drawing memory; numeral 7denotes a display control section; numeral 8 denotes a display; numeral9 denotes a map selecting section; numeral 10 denotes a displayinstructor section; numeral 18 denotes an edit-information holdingsection; and numeral 19 denotes an edit selecting section.

Referring to FIG. 1, the data storage medium 1 stores map data to bedisplayed. The data storage medium 1, for purposes of description, is,but is not limited to, a disc (external storage medium) for storingvarious map data including compressed map data, such as JPEG satellitephotograph data with high compressibility, and uncompressed map data.Other ways of providing stored map data to the system would be known tothose skilled in the art. The data read-out section 2 selects and readsout compressed map data or uncompressed map data from the data storagemedium 1. The data decompressing section 3 reads out the compressed mapdata stored in the data storage medium 1, decompresses it, and storesthe decompressed map data in the first memory 4. On the other hand, forthe uncompressed map data, the data decompressing section 3 stores itunchanged in the first memory 4.

The first memory 4 holds a certain range of map data including thedisplay area of the display 8 in order to display a map on the screen ofthe display 8 and to allow smooth scrolling without delay. This is, forexample, a dynamic random access memory (DRAM), which stores theuncompressed map data read out from the data storage medium 1 by thedata read-out section 2 and the compressed map data decompressed by thedata decompressing section 3.

The drawing memory 6 draws an image to be displayed on the display 8.This is, for example, a video random access memory (VRAM), which issubstantially the same as or larger than the display area of the display8. The drawing section 5 draws the map data stored in the first memory 4into the drawing memory 6. The display control section 7 determines thedisplay area and lets the data for the display area of the drawing areain the drawing memory 6 be displayed in the display 8.

The display instructor section 10 indicates the scaling, the position,the area, and the scrolling of the map to be displayed on the display 8.This includes, for example, a remote control, a joystick, an audioinput, and/or other pointing devices. The map selecting section 9selects a map to be displayed on the display 8, such as a satellitephotograph map and a road map. For example, for a car navigation system,a selecting instruction is inputted for selection depending on whetherthe velocity has exceeded a threshold by a signal from a velocity sensorwhich determines the velocity of the vehicle or through the displayinstructor section 10.

With such an arrangement, when the map is displayed on the display 8 andscrolled in accordance with the instruction of the display instructorsection 10, and when the display range goes out of the map data held inthe first memory 4, the data read-out section 2 newly reads out map datafrom the data storage medium 1 and updates the map data stored in thefirst memory 4.

The display instructor section 10 provides instructions to display andscroll a map to the display control section 7 when a request to displaythe map of a certain point or area, an instruction to scroll thedisplayed map, or an instruction to let the displayed map follow thecurrent location of the vehicle detected by a current location detectorhas been issued from the user with a pointing device, such as a joystickor a mouse, and when the map is scrolled by searching for a car travelroute and simulating travel in accordance with the searched route.

The display control section 7 controls the display on the display 8 withthe central coordinates of the screen and the coordinates ofdrawing-area data corresponding to each other, according to a displayinstruction and the scroll instruction. When the display area is out ofthe drawing area, the display control section 7 reads out map data onthe off-area from the first memory 4 to the drawing section 5 fordrawing, thereby updating the drawing memory 6.

However, when the display area is out of the map data held in the firstmemory 4, the display control section 7 requests the data read-outsection 2 to update the map data, thereby reading out new map data fromthe data storage medium 1 through the data read-out section 2 andrewriting the first memory 4. At that time, when the map data read outfrom the data storage medium 1 is compressed map data, the datadecompressing section 3 decompresses the compressed map data and writesthe decompressed map data in the first memory 4. When the map data isuncompressed map data, the map data is directly written in the firstmemory 4.

The edit-information holding section 18 sets and holds edit informationfor editing the image of a satellite photograph to be displayed on thescreen of the display 8, depending on the evening or night time zone,and the season of spring, summer, fall, and winter. The edit selectingsection 19 selects the edit information held in the edit-informationholding section 18, which senses change information on the environmentand depending on the change information selects edit information for thetime zone such as the evening or night time, the season, and theweather, such as rainy or cloudy weather.

General map data is so-called vector data composed of nodes and links,having drawing element information (identification information aboutroads, buildings, backgrounds, rivers, etc.). On the other hand, rasterdata is bit map data including pixel color information (lightness, hue,chroma, and the values of color-separated RGB), such as photograph datataken from a satellite or an airplane (photograph data taken from thesky) and its processed photograph data. The raster data is divided intoblocks, and each of the divided raster data has representativecoordinates.

The data storage medium 1 stores, for example, uncompressed map data,satellite photograph data that is compressed map data, search data thatis searched for under predetermined conditions, and route data includinga route to a destination as shown in FIG. 2. Among them, the map dataand the search data are uncompressed map data, the map data beingprincipally constituted by a node-link map including background data,such as geographic features, houses, and facilities; road data formed ofroad link data; and name data, such as the names of roads, streets,facilities, and towns, which is a vector data having positioncoordinates.

The satellite photograph data includes position data and image data, asshown in FIG. 3. The image data is high-compressibility raster data,which is formed by compressing raw satellite photograph data by JPEG,such as bit map data. For the raster data, because each of the roads andfacilities has no position coordinates, image data is divided intoblocks, such as image 1, image 2, and image 3, and positionalinformation corresponding to each image data serves as position data.The positional information of each block may be the coordinates of thecenter or the left lower corner of an image, the latitude and longitudeinformation, or alternatively, information in which the latitude andlongitude information is converted to a code. The sizes of images 1, 2,and 3 are basic information common to the images 1, 2, and 3 togetherwith the kind of compression and the compression ratio.

General map display control applied to a navigation system will bedescribed. In a method of reading data around the current location whenimage data of each block is stored with positional information convertedto a code, the coordinates of a drawing area is determined on the basisof the current location and the scale, and raster data contained in thedrawing area is then determined on the basis of the positionalinformation that is obtained from the coordinates of the area and thecode of raster data.

At a normal vehicle speed, satellite photograph data is read out fromthe data storage medium 1 and is decompressed, and the raster data isstored in the first memory 4, so that a map is displayed on the basis ofthe satellite photograph data, on which the current location isdisplayed.

When a vehicle speed exceeds a threshold (for example, 80 km/h), theraster data in the first memory 4 is erased, and uncompressed map datais read out from the data storage medium 1, is held in the first memory4, and is drawn in the drawing memory 6, so that the current location isdisplayed on the vector map data.

Also when the current location is on an expressway, the raster data inthe first memory 4 is erased, and uncompressed map data is read out fromthe data storage medium 1, is held in the first memory 4, and is drawnin the drawing memory 6, so that the current location is displayed onthe vector map data.

As described above, the satellite photograph data is raster compresseddata with high compressibility, thus taking a lot of time fordecompression. Accordingly, the satellite photograph data is convertedto vector uncompressed map data, thereby preventing the map drawing frombeing late during high-speed traveling.

The decompress process and the drawing process for the satellitephotograph data during scrolling will be described. FIG. 4 is a diagramshowing the relationship among satellite photograph data on a datastorage medium, satellite photograph data to be decompressed on a firstmemory, and a display screen; FIG. 5 is a flowchart for displayprocessing; and FIG. 6 is an explanatory diagram of coordinateconversion processing by scrolling a display screen.

Referring to FIG. 4, the satellite photograph data stored in the datastorage medium 1 is divided into blocks A1 to A5, B1 to B5, . . . , E1to E5. In the satellite photograph data, when a display screen a is setacross the blocks A1 to A3, B1 to B3, and C1 to C3 substantially withthe center in the block B2, at least the images of the blocks A1 to A3,B1 to B3, and C1 to C3 are read out from the data storage medium 1, andthe decompressed image data is stored in the first memory 4 (forexample, DRAM).

When a vehicle moves in the direction from the current display screen ato the next display screen b, the images of the blocks B2, B3, C2, andC3 held in the first memory 4 are unchangedly displayed on the movedscreen, and new images of the blocks B4, C4, and D2 to D4 need to bedecompressed from the satellite photograph data and to be stored in thefirst memory 4 for display.

The flow of the display process will be described. Referring to FIG. 5,first, satellite photograph data to be within a drawing area is searchedfor (step S11), and it is determined whether relevant satellitephotograph data exists in the first memory 4 (step S12). When thesatellite photograph data does not exist in the first memory 4,compressed satellite photograph data is read out from the data storagemedium 1 (step S13); the read-out satellite photograph data isdecompressed (step S14); and the decompressed image data is stored inthe first memory 4 (step S15).

When it is determined that the image data exists in the first memory 4,the image data in the first memory 4 is obtained (step S16); the imagedata is drawn in the drawing memory 6 (step S17); and data on thedisplay area is read out from the drawing area and is displayed on thedisplay 8 as an image of the satellite photograph (step S18).

When compressed data for the next display screen is read out from thedata storage medium 1, the data is erased in early order and new data isstored in the first memory 4. Specifically, information unique to themap data of a block (such as positional information and informationabout stored location on the data storage medium 1), which is read outand drawn earlier than the map data of each block to be stored in thefirst memory 4, and information unique to the map data of a block whichis read out later are stored in the first memory 4. Thus, it isdetermined which map data is older by consulting the unique information.

Referring again to FIG. 4, the current location or the cursor sometimesreturns to the area that is once displayed, as from the display screen athrough the next screen b again to the first display screen a. By themethod of erasing the map data of the blocks A1 and A2, when the screenmoves from the next screen b to the first screen a, the blocks A1 and A2are again read out from the data storage medium 1, so that it takes alot of time for processing. On the other hand, giving low erasingpriority to the map data of the blocks A1 and A2 as new map data toprevent it from being erased allows quick display processing withoutrequiring time for repeated reading and decompress processing as the mapdata is held in the first memory 4 even if the display screen is movedas described above.

When a route is displayed on the image of the satellite photograph whichis displayed in this way, among roads of vector data, only a route isoverwritten on the drawing memory 6 in which satellite photograph datais drawn. Also when the current location is displayed, a currentlocation mark is overwritten on the drawing memory 6.

The criteria for drawing are determined depending on the currentlocation, the center of the screen, the user-operated cursor position,etc. In the drawing process, referring to FIG. 6, letting (0, 0) be thecoordinates of the left lower corner of the drawing area, thecoordinates of a previous screen shift to the left lower corner of thedrawing area of the current screen, the coordinates are converted sothat the coordinates (X1, Y1) of the left lower corner of the drawingarea of the current screen becomes (0, 0).

The invention is not limited to the above embodiment, variousmodifications may be made. For example, according to the embodiment,raster data such as satellite photograph data is stored in the datastorage medium 1 as compressed data. However, it is also possible tostructure the system such that vector data or raster data of areas thatmay be used with less frequency is compressed, and vector data or rasterdata of areas that may be used with high frequency is not compressed inthe data storage medium 1. The area that may be frequently used mayinclude a high-density population area, an area having a highway, and anarea having specific facilities and/or major facilities.

Particularly for raster data, it is difficult in actuality to store alluncompressed map data in a data storage medium because it has limitedstorage capacity; on the other hand, storing all the map data withcompression requires decompression every time; thus it takes a lot oftime for display. Accordingly, storing the map data of areas that isassumed to be used with high frequency in the data storage mediumwithout compression decreases display processing and the time fordisplay.

The embodiment in which vector data is stored without compression andraster data is stored with compression has been described; however, thevector data may be compressed as with the raster data.

When a determination is made whether display-area data exists in thefirst memory 4, it is determined, depending on whether the display-areadata exists in the drawing memory 6, as follows. When drawn map data tobe within a new display area exists in the drawing memory 6, thecoordinates of the map data are converted to those of a new screen. Whenno drawn map data to be within a new display area exists in the drawingmemory 6, it is determined whether the data exists in the first memory4, wherein when the data exists, it is read out from the first memory 4and is drawn in the drawing memory 6. When no data exists in the firstmemory 4, compressed map data is read out from the data storage medium 1and is decompressed. The decompressed image data is stored in the firstmemory 4, and the decompressed image data is read out from the firstmemory 4 and is drawn in the drawing memory 6. Display-area data is thenread out from the drawing memory 6 and displayed on the display 8.

It is also possible to employ a map display unit which receives theprogram of the embodiment or, alternatively, a map display unit whichuses a storage medium (IC card) having the program of the embodimentloaded by a personal computer (PC). In such cases, the map display unitincludes a communicating section for transmitting and receiving datato/from an external information center, receiving a program forachieving the functions of the embodiment (refer to the flowchart inFIG. 5 and other embodiments) from the information center, and storingit in a storage medium, such as a hard disk and a flash memory. Thus,the received program is driven to realize the embodiment. Alternatively,a program sent from the information center is downloaded in a storagemedium (IC card) that is detachable from a home PC. Thus, the embodimentcan be achieved by the program driven when the storage medium isinserted into the map display unit.

For the raster data, it is also possible to provide an easily viewabledisplay responding to any difference in the environment using only oneimage data by editing various display images. Specific example of theprocess will be described hereinafter. FIGS. 7(A) to 7(C) are diagramsfor explaining examples of drawing and display processing; FIG. 8 is anexplanatory diagram of an example of the process of converting aday-image satellite photograph to a night image; FIG. 9 is anexplanatory diagram of another example of the process of converting aday-image satellite photograph to a night image; and FIG. 10 is anexplanatory diagram of an example of the process of displaying a markand a route on a satellite photograph.

Edit information to be held in the edit-information holding section 18is as follows. In the case of edit information for editing for theseasons, semi-transparent colors, such as flower-image pink for spring,sky-image blue for summer, autumn-color image yellow for fall, andsnow-image white for winter are set, as in the table of FIG. 7(B), whichare selected depending on the date and are blended to draw the image ofa satellite photograph, and the color (tint) of the satellite photographis thereby changed. In the case of edit information for editing for thetime zone, semi-transparent colors, such as sunset-image red forevening, and dark-image black (in actuality, a “gray tint” to besemi-transparent) for night are set, as in the table of FIG. 7C, whichare selected depending on the time zone and are blended to draw theimage of a satellite photograph, and the color of the satellitephotograph is thereby changed.

In such a case, the edit information may be read out depending on thedata and time to vary the semi-transparent color between spring eveningand spring night and between spring evening and summer evening. Also, inaddition to the environmental changes with a time of noon, evening, andnight and the environmental changes associated with the seasons ofspring, summer, fall, and winter, the color may be varied with theweather of clear, cloudy, and rainy. The weather information may bereceived from the information center; thus, the transparentizing processmay be performed with semi-transparent colors responding to the receivedweather information. The determinations on the time zone and the seasonsare made by receiving global positioning system (GPS) information.

The procedure is as follows. Referring to FIG. 7(A), a drawing area isfirst calculated (step S22), and image data on the drawing area is readout from the first memory 4 and is written to the drawing memory 6 (stepS23). Edit information is read out from the table on the basis of thecurrent data or time, is subjected to transparentizing process (stepS24), and is displayed on the display 8.

When a daytime-image satellite photograph is changed to a night imagephotograph, as in the above, one method (FIG. 8) is to blendsemi-transparent night color (black) (A) onto the image of adaytime-image satellite photograph (B) by combining the data to create asingle night image satellite photograph (C). Referring to FIG. 9,another method is to overlay a semi-transparent layer 1 (A) insemi-transparent black on a layer 2 (B) having an image of a satellitephotograph so that the displayed satellite photograph of the layer 2 isviewed through the overlaid semi-transparent layer 1 to appear as anight image (C). Furthermore, referring to FIG. 10, when a vehicle mark(a bit mapped current location mark) and a searched route (vector-dataguide route) (A) are overlaid on a satellite photograph (C), the vehiclemark and the route (A) are overwritten on the satellite photograph (C)and semitransparent black map data (B) after transparentizing process.

FIG. 11 is a flowchart of a process for switching a display by using onelayer;

FIG. 12 is a flowchart of a process for switching a display by using twolayers; FIG. 13 is a block diagram of a circuit for editing; and FIG. 14is a block diagram of another circuit for editing. In the drawings,reference numeral 5 denotes the drawing section; numerals 6, 6 a, and 6b denote drawing memories; numeral 7 a denotes an editing section;numeral 7 b denotes the display process section; and numeral 8 denotesthe display.

The procedure of the display process shown in FIG. 8, using one layer,is as follows. For example, referring to FIG. 11, it is first determinedwhether the time is day or night by sensing time on the basis of a watchor GPS data, determining lightness, or checking the operationalconditions of the vehicle, such as the operation of a switch and a lightduring night traveling (step S31). It is determined whether the time isday or night (step S32). When it has been determined to be daytime, adaytime satellite photograph is drawn in the drawing memory 6 (step S33)and is displayed on the display 8 (step S37). Describing it with thecircuit of FIG. 13, the data in the drawing memory 6 bypasses theediting section 7 a by means of a switch SW and is displayed on thedisplay 8 through the display process section 7 b.

When it is determined to be night, a daytime satellite photograph isdrawn in the drawing memory 6 (step S34), transmittance is set (stepS35), a semi-transparent satellite photograph image is formed (stepS36), and is displayed on the display 8 (step S37). Describing it withthe circuit of FIG. 13, the data in the drawing memory 6 is edited at atransmittance set by the editing section 7 a, with the switch SW turnedon, into a semi-transparent image and is displayed on the display 8through the display process section 7 b.

The procedure of the display process shown in FIG. 9, using two layers,is as follows. For example, referring to FIG. 12, it is first determinedwhether the time is day or night by determining time and dateinformation on the basis of a watch, GPS data, or a watch corrected byGPS, determining lightness, or checking the operational conditions ofthe vehicle, such as the operations of a switch (ILM switch) and a lightduring night traveling (step S41). It is determined whether the time isday or night (step S42). When it has been determined to be daytime, adaytime satellite photograph is drawn on the layer 1 in the drawingmemory 6 (step S43) and is displayed on the display 8 (step S48).Describing it with the circuit of FIG. 14, the data from the drawingsection 5 is drawn in the first drawing memory 6 a in the image of asatellite photograph, bypasses the editing section 7 a by means of aswitch SW2 and is displayed on the display 8 through the display processsection 7 b.

On the other hand, when it has been determined to be night, a daytimesatellite photograph is drawn on the layer 1 in the drawing memory 6 b(step S44), and is overlaid in a semi-transparent color on the layer 2(step S45); transmittance is set (step S46); the layer 1 and the layer 2are overlaid on one another (step S47); and the overlay is displayed onthe display 8 (step S48). Describing it with the circuit of FIG. 14,with both the switches SW1 and SW2 turned on, the data from the drawingsection 5 is drawn in the image of a satellite photograph in the firstdrawing memory 6 a, and the image in the second drawing memory 6 b isfilled with the semi-transparent color. They are overlaid on one anotherat a transmittance set by the editing section 7 a and displayed on thedisplay 8.

Specific methods of changing a color tone by blend drawing will bedescribed. Let R_(P), G_(P), and B_(P) be the respective editinformation of three primary colors, red (R), green (G), and blue (B),which is to be added as night black and summer blue; R₁, G₁, and B₁, bethe map data of a satellite photograph in pixel units; K be thetransmittance; and A (R_(A), G_(A), and B_(A)) be a fixed value that isdetermined depending on the data and time zone.

One method is to add a value obtained by multiplying transmission-colorinformation by transmittance and a value obtained by multiplying colorinformation of map data by (1−transmittance), which can be expressed asthe following equation:

RGB value (R, G, B) of a transmitted pixel=K×(R_(P), G_(P),B_(P))+(1−K)×(R₁, G₁, B₁).

Another method is to add a value obtained by multiplyingtransmission-color information by transmittance and the colorinformation of map data, which can be expressed as the followingequation:

RGB value (R, G, B) of a transmitted pixel=K×(R_(P), G_(P), B_(P))+(R₁,G₁, B₁).

Still another method is to subtract a fixed value from the colorinformation of map data, which can be expressed as the followingequation:

RGB value (R, G, B) of a transmitted pixel=(R₁, G₁, B₁)−A.

Because general map data is so-called vector data composed of nodes andlinks, and has drawing element information (identification informationon roads, buildings, backgrounds, rivers, etc.), individual color can befreely changed by identifying and selecting each drawing element. On theother hand, raster data is bit map data including color information foreach pixel (lightness, hue, chroma, and the values of color-separatedRGB), such as photograph data taken from a satellite or an airplane(satellite photograph data, etc.) and its processed data. The rasterdata is divided into blocks, and each of the divided raster data hasrepresentative coordinates. Accordingly, roads, buildings, backgrounds,rivers, etc. cannot be identified with such raster data; thus, theembodiment in which a color tone is changed by uniform transparentizingprocess without selecting a drawing element is particularly useful forcontrolling the display of a raster data map.

The satellite photograph data only includes information in whichpositional information of each block is changed to latitude andlongitude information, or information in which the latitude andlongitude information is converted to a code. In order to read the dataaround the current location when the map data of each block is storedwith the positional information changed to a code, a drawing area isdetermined on the basis of the current location, the coordinates of thedrawing area are determined, and raster data corresponding to thedrawing area is determined from the coordinates of the area and thepositional information obtained from the code of the raster data.

According to the embodiment, as described above, semi-transparent color,transmittance, and composition ratio are set or selected, so that thesemi-transparent color of the image of satellite photograph data iscalculated or composed with the set or selected semitransparent color,transmittance, and composition ratio and a semi-transparent image isproduced. Therefore, an easily viewable and familiar display without anoticeable difference can be provided in response to the difference inenvironment, such as evening and night, spring, summer, fall, andwinter, and rainy or cloudy weather using only one piece of massivesatellite photograph data. Thus, a user-friendly map display isrealized. Also, a current location mark, a route, and a user-operatingicon image are simply overwritten on the composite image. Thus, evenwhen a semi-transparent screen is produced from edit informationresponding to various environmental differences, an operating icon imagewith high viewability can be overlaid on a map.

FIG. 15 is a block diagram of a car navigation system incorporating themap display unit according to the embodiment of the invention, whichincludes an input device 11 for inputting information on route guidance;a current-location detector 12 for detecting information on the currentlocation of the vehicle; an information storage device 13 in whichnavigation data necessary for calculating a route, such as satellitephotograph data and road map data, display guidance data necessary forguidance, and a navigation program are stored; a central processing unit14 for performing a display guidance process necessary for a routesearching process and route guidance and for controlling the entiresystem; an information transmitter-receiver 15 for transmitting andreceiving data to/from an information source, such as an informationcenter that stores data necessary for navigation and provides it througha communication line at an operator's request and an electronic databookthat stores map data and data specific to the operator, such asdestination data; and an output device 16 for outputting information onroute guidance. The arrangement of each component will be describedhereinafter.

The input device 11 has a function of instructing the central processingunit 14 to perform navigation by order from the operator so that theoperator can input destination and output voice/screen guide informationas necessary, and includes a touch switch or an operation switch forinputting the destination with a telephone number or the coordinates ona map and requesting route guidance as means for performing thefunction. Of course, the means may be an input device, such as a remotecontrol. Also, it is possible to add a voice recognition device forvoice input and a record-card reader for reading data recorded in an ICcard or an electromagnetic card.

The information transmitter-receiver 15 includes a vehicle informationand communication system (VICS) receiver and a data transmitter-receiveras means for obtaining traffic information. The VICS transmits real-timetraffic information to vehicles by FM multiplex broadcasting (teletextbroadcasting), a radio beacon, or a light beacon. The FM multiplexbroadcasting transmits rough information over a wide area. On the otherhand, the radio beacon and the light beacon provide detailed informationabout a narrow area of about 10 km radius around the beacon, which canbe received when a vehicle passes through the area of the beacon. TheVICS transmission data includes the degree of traffic congestion (suchas impassability, heavy traffic, middle traffic, light traffic, andnormal traffic), the head of congestion, the length of congestion,traffic regulation (construction information, closed traffic, etc.), andtravel time (time required at a prescribed speed) for a link number ofeach road. The data transmitter-receiver is, for example, a cellulartelephone or a personal computer, for transmitting and receivinginformation necessary for navigation to/from a traffic informationcenter (such as an advanced traffic information service: ATIS) at therequest from an operator.

The output device 16 has functions of outputting voice/screen guidanceinformation and print-outputting data processed by the centralprocessing unit 14 when required by the operator, and includes a displayfor displaying the input data and automatically displaying routeguidance at the operator's request on the screen; a printer for printingthe data processed by the central processing unit 14 and the data storedin the information storage device 13; and a speaker for outputting voiceroute guidance.

The display 8 includes a color cathode ray tube (CRT) or a color liquidcrystal display (LCD) acting as the screen of the map display unit ofthe embodiment. The display 8 displays in color all of a satellitephotograph image plane, a route setting plane, a zone plane, anintersection plane necessary for navigation based on the map data andthe guidance data processed by the central processing unit 14, on whicha button for setting the route guidance, switching the guidance planeduring the route guidance is displayed. Particularly, passingintersection information, such as the name of a passing intersection, isviewed as a popup in color on the zone plane. The display is arranged,for example, in an instrumental panel near a driver's seat, so that thedriver, or operator, can know the current location and obtain theinformation on the forward route on the zone plane.

The current-location detector 12 detects information on vehicle'scurrent location, and has an absolute direction sensor including amagnetic field sensor, a steering sensor, a relative direction sensorincluding a gyrocompass, a distance sensor for determining traveldistance from the number of wheel rotations, and a GPS receiver usingthe GPS. Information on time and date and its correction information canbe obtained with the GPS receiver.

The information storage device 13 is an external storage device thatstores a navigation program and data, which is a recording medium, suchas a CD-ROM. The program includes an application section having a mapdrawing section, a route searching section, a route guidance section, acurrent-location calculating section, and adestination-setting-operation control section and outputting navigationsignals; and an operating system, etc, which stores a program for routesearching; programs for display output control necessary for routeguidance and for voice output control necessary for voice guidance; datanecessary therefor; and display information necessary for route guidanceand map display. The data includes raster satellite photograph data;vector map data (a road map, a house map, a building feature map, etc.)necessary for route guidance, intersection data, node data, road data,photograph data, registered point data, destination data, guide roaddata, detailed destination data, destination-read data, telephone-numberdata, address data, and other data files, thus having all data necessaryfor navigation systems.

The central processing unit 14 includes a CPU for performing variousoperations; a flash memory (such as an electrically erasable andprogrammable read-only memory, EEPROM) that is a rewritable nonvolatileROM for storing important information (such as data for setting programsand conditions for route searching and route guidance and variousparameter data); a nonvolatile ROM that stores a program (programreading means) for checking the program of the flash memory and forperforming update processing; and a readable-writable volatile RAM (suchas a static random access memory, SRAM, in which temporarily storedinformation can be electrically held) for temporarily (in a volatilemanner) storing a memory point in which an arbitrary-point informationregistered by the operator, frequency information accumulated by alearning function, and individually stored information, such as errorcorrection information of various detectors. The central processing unit14 further includes an image memory in which image data to be used fordisplay is stored; an image processor for extracting image data from theimage memory in accordance with a display-output control signal from theCPU, applying image processing, and outputting it to the display; and avoice processor for combining a voice, a phrase, a sentence, a sound,etc. that are read out from the information storage device 13 andconverting it to an analog signal under a voice-output control signal,thereby outputting it a speaker.

It is possible to provide a system in which the navigation program anddata is read out from the exterior through the informationtransmitter-receiver 15, or alternatively, a system of a combination ofa vehicle map display unit, a vehicle-mounted navigation unit, and aninformation center. In this way, necessary navigation program and dataare read out from the exterior through the informationtransmitter-receiver 15, so that a necessary program and data can beupdated using a recording medium, such as a DVD, in place of a CD-ROM,as the information storage device 13, and also, they can be directlystored in the flash memory or the RAM of the central processing unit 14without the information storage device 13.

Here the operation will be described. In navigation using the abovearrangement, when the program of the route guidance system is driven bythe CPU of the central processing unit 14, the current-location detector12 first detects the current location, displays a map around the currentlocation, and then sets a destination by means of at least one of atelephone number, an address, a facility name, a memory point, etc.Subsequently, the route from the current location to the destination issearched. When the route has been determined, route guidance and displayare repeatedly performed until reaching the destination while thecurrent location is searched for by the current-location detector 12.The display screen of the embodiment is subjected to a transparentizingprocess depending on the environment, such as the time zone, the season,the driving situation, and the weather, when the satellite photograph isdisplayed.

The edit of the satellite photograph is not limited to the abovedescription and various modifications may be made. The invention hasbeen described with respect to an arrangement in which a drawing memoryin which satellite photograph data is drawn is subjected to atransparentizing process. However, when the satellite photograph data isdrawn in the drawing memory, each pixel of the satellite photograph datais calculated for a transparentizing process; the satellite photographdata may be combined with semitransparent image data; or alternatively,the satellite photograph data may be subjected to logical processingwith operating icon images, such as a current location mark and a routefor overwriting, and then the composed data (edited data) may be drawnin the drawing memory. In other words, the edit process may be performedwith a drawing processor.

Accordingly, varying the color tone of raster map data depending onenvironment allows an easily viewable map to be displayed in a shorttime. Although specific colors have been used in the description, theuse of alternative colors is possible, so long as they aresemi-transparent, to convey the desired information. Such use ofalternative colors falls within the scope of the invention.

According to the invention, map scroll operation can be smoothlyperformed using compressed map data without a delay in the display.

1. A map display unit including a first memory for storing map data anda drawing memory for drawing the map data and displaying display-areadata of a drawing area in the drawing memory on a display, comprising:data-reading means for selectively reading compressed map data anduncompressed map data from a data storage medium; data-decompressingmeans for decompressing the compressed map data read out by thedata-reading means and storing the decompressed map data in the firstmemory; drawing means for drawing either of the uncompressed map dataread out by the data-reading means or the map data stored in the firstmemory in the drawing memory; display-control means for determining thedisplay area and displaying the display-area data of the drawing area inthe drawing memory on the display; and map-selecting means for selectinga map to be displayed, wherein the map-selecting means switches which ofthe uncompressed map data or the map data the drawing means draws in thedrawing memory; wherein the map-selecting means includes means fordetermining the velocity of a vehicle and switches the map to bedisplayed depending on whether the velocity has exceeded a threshold. 2.The map display unit according to claim 1, wherein the compressed mapdata is raster data and the uncompressed map data is vector data.
 3. Themap display unit according to claim 2, wherein the raster data issatellite photograph data.
 4. The map display unit of claim 1, furthercomprising the data storage medium.
 5. A map display method including afirst memory for storing map data and a drawing memory for drawing themap data and displaying display-area data of a drawing area in thedrawing memory on a display, comprising: selectively reading compressedmap data and uncompressed map data from a data storage medium;decompressing the compressed map data read out by the data-reading meansand storing the decompressed map data in a first memory; drawing eitherof the uncompressed map data read out by the data-reading means or themap data stored in the first memory in a drawing memory; determining thedisplay area and displaying the display-area data of the drawing area inthe drawing memory on the display; selecting a map to be displayed;switching which of the uncompressed map data or the map data the drawingmeans draws in the drawing memory; determining the velocity of avehicle; and switching the map to be displayed depending on whether thevelocity has exceeded a threshold.